A window sash running in a resin jamb liner and counterbalanced by springs needs some friction to hold a set position. Without friction, the springs would balance the sash in a position about half open; but friction between the sash and the jamb liner can hold the sash anywhere from closed to wide open. A larger and heavier sash with stronger counterbalance springs needs more friction to hold a set position. Too much friction, however, makes the sash hard to move.
The window art contains many suggestions addressed to the long-standing problem of suitable friction for a spring-balanced, wooden sash; but the proposed solutions all leave several shortfalls. Most friction devices variably expand in the limited space between the jamb liner and the sash stile; but this can deform a resin jamb liner, causing a poor appearance and a possible air leak. Some friction devices are not adjustable so that they have to be made in several sizes for different size windows. Other friction devices can be adjusted only by taking the window apart; and many friction devices are complex, expensive, short-lived, or unreliable.
My sash holder provides sash-holding friction that automatically varies with different sash weights and counterbalance spring forces. My holder is also economical to manufacture, easy to install, and rugged and serviceable. It uses few components, requires no attachment to the sash, and adapts automatically to both upper and lower sashes so as to be practically universal.